Means for localizing tension in running yarn



Dec. 17, 1968 F. c. ALLEN 3,416,206

MEANS FOR LOCALIZING TENSION IN RUNNING YARN Filed March 8, 1965 2 Sheets-Sheet 1 j Dec. 17, 1968 F. C.-ALLEN 3,416,206

MEANS FOR LOCALIZING TENSION IN RUNNING YARN Filed March 8, 1965 2 Sheets-Sheet 2 United States Patent 3,416,206 MEANS FOR LOCALIZING TENSIUN IN RUNNING YARN Frederick C. Allen, Abergavenny, England, assignor to British Nylon Spinners Limited, Pontypool, Monmouthshire, England Filed Mar. 8, 1965, Ser. No. 437,986 Claims priority, application Great Britain, Mar. 12, 1964, 10,434/ 64 Claims. (Cl. 2871.3)

ABSTRACT OF THE DISCLOSURE The tension in a running length of yarn is localized by passing the yarn in contact with a nonrotatable curved surface having a profile with a continuously increasing radius of curvature along at least substantially the entire yarn path.

The invention concerns improvements in or relating to means for localizing tension in running yarn. Such means exert a braking action on yarn that is drawn over or through them to localize the requisite tension.

Although the invention is not to be considered as being limited thereto, one particular instance where tension is required to be localized in a-running yarn is that of drawing synthetic polymer yarns such as those of nylon, as described for instance, in British patent specification No. 543,466. A substantial increase in tension at the tension-localizing device causes the yarn to draw at a neck, i.e. the diameter of the yarn suddenly decreases over a very short length of the yarn, giving the appearance of a neck at that point. Such localisation of the point of draw is of advantage in the production of uniform yarns (eg from the point of view of uniform dyeing).

The tension-localizing means employed in the abovedescribed drawing process is usually a, snubbing pin, around which the yarn is wrapped with one or more turns; and such pin may be heated or unheated, and may be made of metal or of ceramic material.

Whilst such a snubbing pin is invariably the tensionlocalizing means that is actually used, other means have been proposed, such as sheets or plates shaped to present a suitable curved surface convex to the yarn being drawn.

Particularly when yarn is drawn at high draw ratios, for the attainment of maximum tenacity, there is a tendency for filaments to break owing to the high tension and temperature to which the yarn is subjected. Variaticns in the tension of the yarn leaving the pin and also in the final denier of the drawn yarn have often been observed. These variations may be indicative of a tendency to overdrawing, which in turn may lead to filament breaks.

We have discovered that these variations may be reduced in certain yarns if a tension-localizing means of the type described hereafter is used instead of the normal circular cross-section snubbing pin.

According to the invention means for localizing tension in a running yarn comprises a non-rotatable curved surface around and in contact with which the yarn is pulled under tension and having a profile with a continuously increasing radius of curvature along at least substantially the entire yarn path.

A presently preferred tension-localizing means according to the invention is one in which the profile is a logarithmic spiral such that the yarn makes one wrap around the profile and such that the normal force exerted on the yarn in contact with the surface does not increase at so high a rate as on a circular pin and does not reach such high final values. Such a means can be made from stainless steel bar, channelled and mattchromed around its exterior yarn-contacting surface, the bar being mounted "ice on a pin attached to it at right angles at the beginning of the spiral, i.e. at the point of minimum radius, Where first the yarn contacts the channelled exterior surface. At the other end of the track, the yarn-contacting surface may be straight over a short distance along the yarn path; and such short, straight portions may also exist at other locations around the yarn path, so as to allow for localisation of different tensions around the yarn path. The steel bar is slightly helically shaped, in the axial direction of the mounting pin, in order to separate the incoming yarn path from the outgoing path.

Alternatively, such a means can be made from a stainless steel plate, in which case the yarn will take up a path providing the most intimate contact between the surface of the yarn and that of the plate, in which respect the plate may have a slight advantage over the channelled bar.

The profile of this presently preferred tension-localizing means is worked out from the formula: r=Ae where, r is the radius of curvature of the means at the normal which forms an angle 6 with the normal at the point of initial contact of the yarn,

k is a constant,

A is a constant The main advantages of such a logarithmic profile tensionlocalizing means, when such is employed to localize the drawing tension in certain nylon yarns, are that it leads to a reduction in denier variation along the yarn when such is drawn at high speeds and high draw ratios, and that the maximum attainable draw ratio is increased. A subsidiary advantage may be that it reduces the rate of tension increase, thereby reducing the concentration of stress and strain at any point.

Yet anotheer advantage relates to the reduction in the number of nubs in synthetic monofilament yarns. Nubs are short lengths of undrawn yarn in the drawn monofilament yarns, normally to be regarded as defects downgrading the quality of the yarn if present in any great number in 10 feet lengths of yarn. One way of decreasing the number of nubs is to increase the distance between the snubbing-pin and the draw roll, but this leads to an inconvenient disposition of the pieces of apparatus on a production machine. By using a snubbing-pin having a logarithmically profiled metal track, according to the invention, the nub level can be maintained very low at ordinary snubbing-pin-to-draw-roll distances.

The preferred tension means also has a further advantage over a circular cross-section cylindrical snubbing pin, for instance, in that it is possible to apply heating or cooling to the means at any part or parts of the yarn path around the track, without necessarily affecting the temperature of other parts of the path. This is important too, in that there need be no feed-back of heat from the yarn departure point along the yarn path to the entry point.

The invention will now be described with reference to the accompanying drawings, in which FIGURE 1 is a diagram of the yarn path approaching and in the drawing zone of a drawing machine, showing preferred means for localizing the drawing tension according to invention;

FIGURE 2 is a side perspective view of the preferred tension-localizing means having a logarithmic spiral profile;

FIGURE 3 is a view of such a means, on a larger scale, showing means for heating and/ or cooling it;

FIGURE 4 is a perspective view of another version of the preferred tension-localizing means.

FIGURE 1 shows a tension-localizing means 1 used as the snubbing-pin of a drawing machine. The means takes the form of a channelled metal bar 2 mounted on a pin 3 and shaped to a profile of a logarithmic spiral. On this machine a supply package 5 of undrawn yarn Y is mounted at the top of the machine on a creel (not shown). The yarn is withdrawn over one end of the supply package around guide 7 and thence passes downwardly through pig-tail guide '9. From the guide, the yarn is drawn by driven feed rolls, comprising roll 11 and nip roll 13, and is passed thereby into the drawing zone.

The undrawn yarn is drawn in the drawing zone by being pulled under tension by driven draw roll 15, rotating at a peripheral speed greater by the required draw ratio than that of feed roll 11, around which draw roll 15 and its idler separator roll 17, the drawn yarn is wrapped three times as shown. The point of draw is located on the tension localizing means 1, around the major proportion of whose outer curved and channeled surface the yarn is wrapped whilst its path is turned through 360.

From draw roll 15, the draw yarn is forwarded to a wind-up means (not shown).

FIGURE 2 shows the preferred tension-localizing means on a larger scale. The channelling 19 in the outer curved surface of the channelled member 2, providing a track for the yarn, is clearly visible, and so is the mounting pin 3 at the yarn input end of the track. The helical nature of the member 2 is also clear.

In FIGURE 3, the manner in which the yarn may join and depart from the tension-localizing means is shown in greater detail. Metal tubes 21, fitted within tubular metal holders 23, are located at intervals along and in contact with the inside of the channeled member 2 providing the yarn track. Cartridge heaters may be fitted within any or all of said tubes, to heat the local area of the yarn track; or heating or cooling fluids may be circulated through the tubes to provide any desired temperature gradients along the track.

In FIGURE 4, the tension-localizing means is similar to that of the other figures save that it comprises a metal plate 25 shaped to a profile of a logarithmic spiral.

As an example of the invention, a logarithmic spiral stainless steel track tension-localizing means according to the invention having the value of k=.25, and A=.4 was compared with other tension-localizing means in the drawing of 120 denier monofilament polyhexamethylene adipamide at 3,300 feet/minute and at a draw ratio of 6.6. (It was not possible to compare the performance of Sintox snubbing-pins, because with both 1 inch and /8 inch diameter circular cross-section pins of that material the yarn broke down continuously.)

The comparison is made in the following table:

N o. of changes (i.e., the re- Overall denier versals of direcvariation tion of denier (Percent of variation) per Tension-localizing means The drawn yarn produced with the logarithmic spiral track had an extensibility of about 13% and a tenacity of 9-10 grams/denier.

It is important to keep the coefficient of friction between the yarn and the tension-localizing means as low as possible, as by a matt-chromed surface of the means, subject to the proviso that the tension in the yarn upstream of the means shall not be allowed to be so great, in a drawing process, that drawing actually occurs upstream of the means rather than in contact with it.

Although the invention has been particularly described with reference to the drawing of nylon yarns, it is equally applicable to drawing processes for other synthetic polymer yarns, such as those of polyester or polypropylene material. Furthermore, as mentioned above, the invention is not confined to use within a drawing process, but may be used whenever tension is required to be localized in a gradual, uniformly increasing manner in a running yarn, whether that yarn be a monofilament or a multifilament yarn. Naturally, however, it is in the critically sensitive drawing process for synthetic polymer yarns that the invention has its greatest applicability.

What I claim is:

1. Means for localizing tension in a running yarn comprising a non-rotatable curved spiral surface around and in contact with which the yarn is pulled under tension and said spiral having a profile with a continuously increasing radius of curvature along at least substantially the entire yarn path.

2. Means according to claim 1 and having heating means incorporated therewith for heating at least a part of said surface.

3. Means according to claim 1 and having cooling means incorporated therewith for cooling a part of said surface not heated by said heating means.

4. Means for localizing tension in a running yarn comprising a non-rotatable curved surface around and in contact with which the yarn is pulled under tension, said curved surface having a logarithmic spiral profile with continuously increasing radius of curvature along at least substantially the entire yarn path.

5. Means according to claim 4 in which the curved surface is provided by a channelled member, the channel in which constitutes a yarn track.

6. A process for localizing tension in a running yarn comprising the steps of (a) continuously pulling a yarn from a supply there- (b) contacting said yarn over a portion of its length,

whilst it is being so pulled, with a non-rotatable curved surface having a profile with a continuously increasing radius of curvature along at least substan tially the entire yarn path, and

(c) wrapping said yarn around and in contact with said surface.

7. A process according to claim 6 in which undrawn synthetic polymeric yarn is pulled around and in contact with said surface under a tension suflicient to draw it, and in .which the yam draws in contact with said surface.

8. A process according to claim 7 in which the yarn is heated over a portion of its travel in contact with said surface.

9. A process for localizing tension in a running yarn comprising the steps of (a) continuously pulling the yarn from a supply thereof, (b) contacting said yarn over a portion of its length, while it is being so pulled, with a non-rotatable curved logarithmic spiral surface, having a profile with a continuously increasing radius of curvature along at least substantially the entire yarn path and (c) wrapping said yarn around and in contact with said surface.

10. A process according to claim 9 in which the yarn is heated by contact with a heated portion of said surface.

References Cited UNITED STATES PATENTS 2,993,260 7/1961 Boerma et a1. 2862 3,083,523 4/1963 Dahlstrom et al. 161172 3,099,872 8/1963 Siggel et a1. 28-713 3,108,323 10/1963 Sikorski 2S7l.3 X 3,256,134 6/1966 Rice 16l-l72 3,277,228 10/1966 Killoran et a1 264-290 LOUIS K. RIMRODT, Primary Examiner.

US. Cl. X.R. 

